Polyvinyl chloride (PVC) is a well-known synthetic polymer. PVC has many qualities that make it a desirable building material. For example, it can be manufactured to be rigid or with a range of flexibility, it is resistant to moisture and mildew, waterproof and easily washable, and it is very durable. Rigid PVC is commonly used in construction for piping, doors and windows, and other applications where it replaces wood, metal, and other rigid materials. In the prior art, PVC is made flexible by adding plasticizers to the mixture of PVC components during manufacture. The most widely used plasticizers are phthalates, (which recent research has determined are toxic). In its flexible form, PVC is used in electrical cable insulation, imitation leather, signage, and other applications where it can take the place of rubber, leather, and other non-rigid materials. PVC is also resistant to impacts, aging, cracking, warping, and discoloration.
Because of its desirable characteristics, PVC has many commercial uses. For example, sheets of PVC are used as a flooring material, interior paneling, and exterior siding. As a flooring material, PVC is comfortable to walk on, and can have a very durable surface layer that resists slipping, even when wet. It can be produced to have a rich variety of colors, designs, and simulations of other materials. For example, PVC flooring is available that is similar in appearance to carpet, stone, wood, and tile, including a surface that can be embossed to enhance the realism of the simulation. The surface may alternatively be made flat, with a rough, matte, or glossy finish. PVC sheets can also be manufactured to have one or more visible design layers to achieve various effects, using a very broad palette of colors in virtually any hue, saturation, and tone from muted to brilliant. Adjacent contrasting areas can be formed and/or machined to have very precisely controlled shapes and colors.
Because of all of these traits, PVC board is superior to other common construction materials, particularly inside wall paneling and flooring material, and can give full play to designer creativity. It can meet the unique needs of virtually any decor. In addition, PVC can be made to be sound absorbent, reducing ambient noise by as much as 20 decibels; and can be made to mitigate noise from percussion events such as walking in high heels. This makes PVC particularly suited to quiet environments such as hospitals, libraries, lecture halls, theaters, and the like.
Moreover, PVC is easy to work with. As a wood replacement, it can be worked like wood by drilling, sawing, nailing, planing, gluing, and other processing; and it provides similar performance, such as nail holding power. Products made of PVC are also normally at least as easy to install as those made with other materials. It is strong and light, and parts with mating connections can easily be assembled with adhesive made for bonding PVC and, in a relatively short time, the bond is as strong as the PVC body.
However, PVC production in the prior art is complicated. It requires a large number of processing steps, all of which must be tightly controlled and performed in a set order. For example, producing PVC boards generally involves mixing together in separate steps PVC powder, plasticizers, stabilizers, lubricants, fillers, and other raw materials. At each step, the materials must be completely and uniformly mixed to produce a consistent mixture. After the PVC material is produced, forming it into finished products typically entails first making sheets of PVC. This also requires numerous ordered steps, involving rolling semi-finished product into component sheets, combining the sheets in one or more separate processes resulting in a finished sheet that has many layers, and processing the layered sheets into finished products. If the layers are not firmly affixed to each other, they may separate, bubble, crack, or otherwise be of a lesser quality than desired.
Existing PVC production methods generally include separate steps for mixing, stabilizing, sealing, curing, tempering, coating, laminating, and more. Combining and mixing constituent raw materials, such as PVC powder, plasticizers, stabilizers, lubricants, fillers and others, typically must be added in a certain order. Products having layers with different characteristics require each layer to be mixed separately from the others. Each such layer may be milled into an intermediate stage by rolling the PVC into sheets, and the sheets must then be combined in a certain order, and fused together into a combined sheet, often by one or more heating steps. The combined sheet is then typically cut to shape and molded to form if needed. The PVC may be cured under ultraviolet light, and may be tempered by a plurality of heating, stretching, and cooling steps. In some applications, the PVC must also be laminated. Further steps can include forming designs or patterns on one or more layers, texturing one or more surfaces, and the like. Thus, the PVC manufacturing process is quite complex.